High-Resolution Mapping of the Physical Location of the Tomato Cf-2 Gene. M. S. Dixon. Sainsbury Laboratory, John Innes Centre for Plant Science Research, Colney Lane, Norwich, NR4 7UH, England. D. A. Jones (1), K. Hatzixanthis (1), M.W. Ganal (2,3), S. D.Tanksley,(3) and J. D. G. Jones(1) (1)Sainsbury Laboratory, John Innes Centre for Plant Science Research, Colney Lane, Norwich, NR4 7UH, England; (2)Institute for Plant Genetics and Crop Plant Research, Gatersleben, Germany; (3)Department of Plant Breeding and Biometry, 252 Emerson Hall, Cornell University, Ithaca, NY 14853 U.S.A. MPMI 8:200-206. Accepted 1 December 1994. Copyright 1995 The American Phytopathological Society.

To isolate the tomato Cf-2 resistance gene by map-based cloning, plants recombinant for RFLP markers close to Cf-2 were selected by exploiting the flanking morphological markers yv (yellow virescent) and tl (thiaminless). Using these recombinants, a high-resolution linkage map of the region encompassing the Cf-2 gene has been generated containing several new RFLP markers. Mapping of two YAC clones carrying Lycopersicon esculentum and L. pe-ruvianum DNA, indicates that in both genotypes the physical distance between the two closest flanking markers is less than 40 kb. This study also positions Cf-2 relative to the Mi gene, which confers resistance to root-knot nema-todes.